An energy-saving static bandwidth allocation method for link rate configurable passive optical networks

Abstract

The present invention discloses an energy-saving static bandwidth allocation method for a link rate configurable passive optical network. The method first records the modulation format, working channel and allocated bandwidth of the currently online ONU through the OLT; and simultaneously records the remaining time slot t of each working channel. j , channel response and the ONU set allocated on each working channel; then monitor the request messages sent by each ONU to register online or cancel offline in real time, and then make different static bandwidth allocation adjustments according to different request messages. In the entire static bandwidth allocation adjustment process, the calculation complexity is reduced by controlling the number of adjustments, and at the same time, the channel bandwidth resources in the passive optical network can be better utilized.

Description

Technical Field

[0001] The present invention belongs to the technical field of passive optical networks, and more particularly, relates to an energy-saving static bandwidth allocation method for a link rate configurable passive optical network. Background Art

[0002] With the rapid increase in backbone network bandwidth and the rapid growth of local area networks, the bottleneck of access networks has become an increasingly large gap between the two. Passive Optical Network (PON) is regarded by many as an effective solution for the "first mile" access network.

[0003] The PON infrastructure consists of three main components: the centrally located optical line terminal (OLT), the optical network unit (ONU), and the optical distribution network (ODN). In downstream transmission, the OLT sends broadcast frames, and each ONU selectively receives data frames sent to it. In upstream transmission, time division multiple access (TDMA) is used to prevent conflicts between different data frames. Each ONU sends frames according to the bandwidth allocation window from the OLT.

[0004] Dynamic Bandwidth Allocation (DBA) is a key technology in PON systems. It allocates bandwidth based on the real-time traffic demands of ONUs, ensuring efficient bandwidth utilization and supporting high-efficiency network operation. In the event of network overload or congestion, DBA enables real-time adjustments to bandwidth allocation to maintain the quality of service for critical services.

[0005] In traditional passive optical networks (PONs), physical layer data transmission and MAC layer network management are independent functions. Traditional DBA algorithms use a fixed, uniform link transmission rate on the channel to send traffic to ONUs. With the advancement of physical layer technology, the traditional single-link-rate optical signal transmission method is being replaced by more complex and variable software-defined methods. In configurable link-rate PONs, PONs combine physical and MAC layer technologies to allow different ONUs to select appropriate channel link rates based on their physical layer channel quality, representing the future of new PONs. Targeting future application scenarios, configurable link-rate PONs utilize a combined physical layer and MAC layer bandwidth allocation algorithm. This algorithm takes into account the variability of ONU transmission quality and not only allocates transmission bandwidth to each ONU according to conventional algorithms, but also assigns each ONU a working channel and link transmission rate. By assigning different working channels and link transmission rates to different ONUs, this combined physical layer and MAC layer bandwidth allocation algorithm increases the capacity of optical access networks.

[0006] The physical layer and MAC layer bandwidth allocation algorithm uses a combination of static and dynamic bandwidth allocation to effectively improve system transmission capacity and performance. First, when an ONU registers with the system, static bandwidth allocation is completed. Based on the ONU's basic bandwidth and physical layer characteristics such as channel insertion loss, the ONU is assigned a suitable working channel and its link transmission rate is determined. Second, after static bandwidth allocation is completed, the online ONU assigned to each working channel is determined. Then, a dynamic bandwidth allocation algorithm based on weight coefficients is used to complete time slot allocation for each ONU on the channel based on the ONU's current data cache status, enabling data transmission.

[0007] PON systems that support configurable link rates use static bandwidth allocation schemes to effectively improve system transmission efficiency. However, static bandwidth allocation schemes also have some problems. In actual optical networks, the traffic of ONUs fluctuates over time, and the bandwidth required by them also changes continuously. As the number of online ONUs decreases, the total ONU bandwidth also decreases, and the bandwidth resources available for allocation on each channel increases. At this time, online ONUs can adjust their operating channels to achieve higher transmission rates and thus better transmission performance. At the same time, they can also shut down some idle channels to reduce system energy consumption. However, this may cause the ONUs to frequently switch between different channels. Therefore, to adapt to changes in network traffic, static bandwidth allocation schemes need to be appropriately adjusted to achieve better system transmission efficiency and performance.

[0008] One type of static bandwidth allocation scheme is a fixed static bandwidth allocation scheme. A fixed static bandwidth allocation scheme means that the OLT only performs static bandwidth allocation when an ONU registers online. After that, the ONU is assigned a fixed working channel and cannot adjust the channel. Static bandwidth allocation ends when the ONU logs off. This approach has the advantage of lower computational complexity for static bandwidth allocation, as each ONU only performs static bandwidth allocation once when it registers online. However, the inability to adjust channels can lead to a situation where, initially, a large number of ONUs come online, using almost all channels for bandwidth allocation. As more ONUs go offline, the remaining bandwidth on each channel increases. However, the online ONUs cannot adjust their working channels and continue to use the initially allocated working channels. In this scenario, only a small number of ONUs are on most working channels, and only a small amount of bandwidth resources are utilized, wasting a large amount of bandwidth resources. Furthermore, the large number of working channels used results in high energy consumption.

[0009] Another static bandwidth allocation scheme involves adjusting the static bandwidth allocation every time an ONU registers or logs off. Each time an ONU goes online or offline, all ONUs undergo a new static bandwidth allocation to achieve optimal performance. This scheme achieves static bandwidth allocation using the minimum number of channel time slots and active channels, effectively utilizing channel bandwidth resources and reducing energy consumption. However, this scheme has high computational complexity, and ONUs exchange control messages with the OLT when adjusting their active channels and modulation formats. During this period, the ONUs cease operations, resulting in significant control overhead and adjustment time. Summary of the Invention

[0010] The present invention aims to overcome the shortcomings of the prior art and provide an energy-saving static bandwidth allocation method for a link rate configurable passive optical network. The static bandwidth allocation is adjusted at most once each time an ONU goes online or offline. This reduces computational complexity by controlling the number of adjustments and makes better use of channel bandwidth resources.

[0011] To achieve the above-mentioned object of the invention, the present invention provides an energy-saving static bandwidth allocation method for a link rate configurable passive optical network, characterized by comprising the following steps:

[0012] (1) Record the current status of the passive optical network;

[0013] In a passive optical network, the optical line terminal (OLT) records the modulation format, working channel, and allocated bandwidth of the currently online optical network unit (ONU). At the same time, the OLT records the remaining time slots t of each working channel in the passive optical network. j, channel response and the set of ONUs allocated on each working channel, j = 1, 2, ..., M, where M is the number of working channels; when there is no ONU on a working channel, the remaining time slots of the channel are initialized to the bandwidth allocation period T DBA ;

[0014] (2) Select static bandwidth allocation schemes with different strategies based on ONU requests;

[0015] In a passive optical network, each ONU is monitored in real time. When an ONU needs to register online or log off offline, it will send a request message to the optical line terminal OLT. After receiving the request message sent by an ONU, the OLT first determines whether the content of the request message is a request to go online or a request to go offline. If it is a request to go online, it goes to step (3); if it is a request to go offline, it jumps to step (4);

[0016] (3) Adjustment of static bandwidth allocation when ONU goes online and registers;

[0017] (3.1) Assume that the ONU sending the request message is numbered k; the OLT reads the request message content and extracts the requested bandwidth B of the kth ONU. k and insertion loss λ k ;

[0018] (3.2) OLT performs static bandwidth allocation for ONU No. k;

[0019] (3.2.1) Sort the M working channels from 1 to M according to the channel response from high to low, set the jth working channel as the initial allocation channel of the kth ONU, and initialize j = 1;

[0020] (3.2.2) According to the insertion loss λ of the kth ONU k and the channel response of the jth working channel, determine the modulation format of the kth ONU on the jth working channel, and then calculate the link rate V of the kth ONU on the jth working channel k,j ;

[0021] (3.2.3) Determine the remaining time slot t on the jth working channel j Is the bandwidth B sufficient to send the kth ONU? k , that is: t j ×V k,j ≥B k ×T DBA Is it satisfied? If so, go to step (3.2.4); otherwise, go to step (3.2.5);

[0022] (3.2.4) Set the jth working channel as the working channel of the kth ONU, and set the kth ONU to the working channel according to the modulation format and working link rate V k,j Complete static bandwidth allocation, and the allocated static bandwidth is B k , the allocated time slot is T k =T DBA ×B k / V k,j At the same time, add the kth ONU to the ONU set on the jth working channel and update the remaining time slots of the jth working channel

[0023] (3.2.5) Replace the j+1th working channel and perform bandwidth allocation for ONU No. k again according to steps (3.2.2) to (3.2.4); after all working channels are replaced, if all working channels cannot complete bandwidth allocation for ONU No. k, it means that ONU No. k has failed to go online and register, and the OLT abandons this static bandwidth allocation adjustment;

[0024] (4) Adjustment of static bandwidth allocation when ONU goes offline;

[0025] (4.1) Assume that the ONU sending the request message is numbered k; the OLT reads the request message content and extracts the modulation format, working channel and allocated bandwidth B of the kth ONU. k ;

[0026] (4.2) OLT logs off the kth ONU;

[0027] Assuming that ONU No. k is offline on working channel No. q, the transmission link rate V of ONU No. k is calculated based on the modulation format of ONU No. k on working channel No. q. k,q , OLT allocates bandwidth B k Update the remaining time slots of the qth working channel t q The remaining time slots of the qth working channel before the update; at the same time, the kth ONU that has been offline is deleted from the ONU set of the qth working channel; after that, the modulation format and working channel are no longer selected for the kth ONU that has been offline, and the allocated bandwidth B is k becomes 0;

[0028] (4.3) The OLT performs static bandwidth allocation on the ONUs that are still online.

[0029] (4.3.1) Sort the M working channels from 1 to M according to the channel response from high to low, and then find the working channel with the lowest channel response for the ONU currently working online;

[0030] (4.3.2) Find the ONU set in the working channel with the lowest channel response, sort the ONUs in the ONU set from high to low according to their insertion loss and number them from 1 to N, then go to step (4.4) and re-allocate static bandwidth to the numbered ONUs in turn;

[0031] (4.4) The OLT re-allocates static bandwidth for the nth ONU, where n = 1, 2, ..., N, and initializes n = 1;

[0032] (4.4.1) Set the jth working channel as the initial allocation channel of the nth ONU, and initialize j = 1;

[0033] (4.4.2) Based on the insertion loss of ONU No. n and the channel response of working channel No. j, determine the modulation format of ONU No. n on working channel No. j, and then calculate the link rate V of ONU No. n on working channel No. j. n,j ;

[0034] (4.4.3) Determine the remaining time slot t on the jth working channel j Is the bandwidth B sufficient to send the nth ONU? n , that is: t j ×V n,j ≥B n ×T DBA Is it satisfied? If so, go to step (4.4.4); otherwise, go to step (4.4.5);

[0035] (4.4.4) Set the jth working channel as the working channel of the nth ONU, and set the modulation format and link rate V of the nth ONU on the jth working channel. n,j Complete static bandwidth allocation, and the allocated static bandwidth is B n , the allocated time slot is T j =T DBA ×B n / V n,j ; Add the nth ONU to the ONU set on the jth working channel and update the remaining time slots of the jth working channel At the same time, the nth ONU is deleted from the ONU set in the working channel with the lowest channel response, and the remaining time slots of the working channel with the lowest channel response are updated. t 低 is the remaining time slot of the working channel with the lowest channel response before updating, V n,低 Indicates the link rate of ONU No. n on the working channel with the lowest channel response;

[0036] Replace the n+1th ONU and perform bandwidth allocation for the n+1th ONU again according to steps (4.4.1) to (4.4.4) until bandwidth allocation for N ONUs is completed;

[0037] (4.4.5) Change the j+1th working channel and complete the bandwidth allocation of the nth ONU on the j+1th working channel according to steps (4.4.1) to (4.4.4), and so on;

[0038] (4.5) After N ONUs complete the static bandwidth allocation of all working channels, observe whether the total number of working channels used by all online ONUs in the passive optical network decreases. If the total number of working channels decreases, the OLT saves the result of this static bandwidth allocation; otherwise, the OLT abandons this static bandwidth allocation.

[0039] The object of the invention of the present invention is achieved like this:

[0040] The present invention provides an energy-saving static bandwidth allocation method for a link rate configurable passive optical network. The method first records the modulation format, working channel and allocated bandwidth of the currently online ONU through the OLT; and simultaneously records the remaining time slot t of each working channel. j , channel response and the ONU set allocated on each working channel; then monitor the request messages sent by each ONU to register online or cancel offline in real time, and then make different static bandwidth allocation adjustments according to different request messages. In the entire static bandwidth allocation adjustment process, the calculation complexity is reduced by controlling the number of adjustments, and at the same time, the channel bandwidth resources in the passive optical network can be better utilized. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a flow chart of an energy-saving static bandwidth allocation method for a link rate configurable passive optical network according to the present invention;

[0042] Figure 2 This is a comparison chart of the average number of used channels for different solutions. DETAILED DESCRIPTION

[0043] The following describes the specific embodiments of the present invention in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when detailed descriptions of known functions and designs may dilute the main content of the present invention, such descriptions will be omitted here.

[0044] Example

[0045] Figure 1 The present invention is a flow chart of an energy-saving static bandwidth allocation method for a link rate configurable passive optical network.

[0046] In this embodiment, if Figure 1 As shown, the energy-saving static bandwidth allocation method of the link rate configurable passive optical network of the present invention includes the following steps:

[0047] (1) Record the current status of the passive optical network;

[0048] The infrastructure of a passive optical network consists of three main components: the optical line terminal (OLT), the optical network unit (ONU), and the optical distribution network (ODN). The OLT and ONU are connected via a physical transmission medium. Each OLT has a fixed number of connected ONUs. The OLT is responsible for allocating upstream bandwidth and managing ONU registration. The ONU directly interfaces with user terminals, providing them with an interface to access the optical network.

[0049] The optical line terminal OLT records the modulation format, working channel and allocated bandwidth of the currently online optical network unit ONU; at the same time, the OLT records the remaining time slot t of each working channel in the passive optical network. j , channel response and the set of ONUs allocated on each working channel, j = 1, 2, ..., M, where M is the number of working channels; when there is no ONU on a working channel, the remaining time slots of the channel are initialized to the bandwidth allocation period T DBA ;

[0050] (2) Select static bandwidth allocation schemes with different strategies based on ONU requests;

[0051] In a passive optical network, a low-complexity energy-saving static bandwidth allocation adjustment scheme considers different strategies when an ONU goes online or offline. When an ONU needs to register online or log off offline, it sends a request message to the optical line terminal (OLT). After receiving the request message sent by an ONU, the OLT first determines whether the content of the request message is a request to go online or a request to go offline. If it is a request to go online, it goes to step (3); if it is a request to go offline, it jumps to step (4).

[0052] (3) Adjustment of static bandwidth allocation when ONU goes online and registers;

[0053] (3.1) Assume that the ONU sending the request message is numbered k; the OLT reads the request message content and extracts the requested bandwidth B of the kth ONU. k and insertion loss λ k ;

[0054] (3.2) OLT performs static bandwidth allocation for ONU No. k;

[0055] (3.2.1) Sort the M working channels from 1 to M according to the channel response from high to low. For working channels with the same channel response, the working channel with the lower frequency is used first. Set the jth working channel as the initial allocation channel for the kth ONU, and initialize j = 1.

[0056] (3.2.2) According to the insertion loss λ of the kth ONU k and the channel response of the jth working channel, determine the modulation format of the kth ONU on the jth working channel, and then calculate the link rate V of the kth ONU on the jth working channel k,j ;

[0057] (3.2.3) Determine the remaining time slot t on the jth working channel j Is the bandwidth B sufficient to send the kth ONU? k , that is: t j ×V k,j ≥B k ×T DBA Is it satisfied? If so, go to step (3.2.4); otherwise, go to step (3.2.5);

[0058] (3.2.4) Set the jth working channel as the working channel of the kth ONU, and set the kth ONU to the working channel according to the modulation format and working link rate V k,j Complete static bandwidth allocation, and the allocated static bandwidth is B k , the allocated time slot is T k =T DBA ×B k / V k,j At the same time, add the kth ONU to the ONU set on the jth working channel and update the remaining time slots of the jth working channel

[0059] (3.2.5) Replace the j+1th working channel and perform bandwidth allocation for ONU No. k again according to steps (3.2.2) to (3.2.4); after all working channels are replaced, if all working channels cannot complete bandwidth allocation for ONU No. k, it means that ONU No. k has failed to go online and register, and the OLT abandons this static bandwidth allocation adjustment;

[0060] (4) Adjustment of static bandwidth allocation when ONU goes offline;

[0061] (4.1) Assume that the ONU sending the request message is numbered k; the OLT reads the request message content and extracts the modulation format, working channel and allocated bandwidth B of the kth ONU. k ;

[0062] (4.2) OLT logs off the kth ONU;

[0063] Assuming that ONU No. k is offline on working channel No. q, the transmission link rate V of ONU No. k is calculated based on the modulation format of ONU No. k on working channel No. q. k,q , OLT allocates bandwidth B k Update the remaining time slots of the qth working channel t q The remaining time slots of the qth working channel before the update; at the same time, the kth ONU that has been offline is deleted from the ONU set of the qth working channel; after that, the modulation format and working channel are no longer selected for the kth ONU that has been offline, and the allocated bandwidth B is k becomes 0;

[0064] (4.3) The OLT performs static bandwidth allocation on the ONUs that are still online.

[0065] (4.3.1) Sort the M working channels from 1 to M according to the channel response from highest to lowest. For working channels with the same channel response, the one with the lowest frequency will be used first. Then find the working channel with the lowest channel response that currently has an ONU working online.

[0066] (4.3.2) Find the ONU set in the working channel with the lowest channel response, sort the ONUs in the ONU set from high to low according to their insertion loss and number them from 1 to N, then go to step (4.4) and re-allocate static bandwidth to the numbered ONUs in turn;

[0067] (4.4) The OLT re-allocates static bandwidth for the nth ONU, where n = 1, 2, ..., N, and initializes n = 1;

[0068] (4.4.1) Set the jth working channel as the initial allocation channel of the nth ONU, and initialize j = 1;

[0069] (4.4.2) Based on the insertion loss of ONU No. n and the channel response of working channel No. j, determine the modulation format of ONU No. n on working channel No. j, and then calculate the link rate V of ONU No. n on working channel No. j. n,j ;

[0070] (4.4.3) Determine the remaining time slot t on the jth working channel j Is the bandwidth B sufficient to send the nth ONU? n , that is: t j ×V n,j ≥B n ×T DBAIs it satisfied? If so, go to step (4.4.4); otherwise, go to step (4.4.5);

[0071] (4.4.4) Set the jth working channel as the working channel of the nth ONU, and set the modulation format and link rate V of the nth ONU on the jth working channel. n,j Complete static bandwidth allocation, and the allocated static bandwidth is B n , the allocated time slot is T j =T DBA ×B n / V n,j ; Add the nth ONU to the ONU set on the jth working channel and update the remaining time slots of the jth working channel At the same time, the nth ONU is deleted from the ONU set in the working channel with the lowest channel response, and the remaining time slots of the working channel with the lowest channel response are updated. t 低 is the remaining time slot of the working channel with the lowest channel response before updating, V n,低 Indicates the link rate of ONU No. n on the working channel with the lowest channel response;

[0072] Replace the n+1th ONU and perform bandwidth allocation for the n+1th ONU again according to steps (4.4.1) to (4.4.4) until bandwidth allocation for N ONUs is completed;

[0073] (4.4.5) Change the j+1th working channel and complete the bandwidth allocation of the nth ONU on the j+1th working channel according to steps (4.4.1) to (4.4.4), and so on;

[0074] (4.5) After N ONUs complete the static bandwidth allocation of all working channels, observe whether the total number of working channels used by all online ONUs in the passive optical network decreases. If the total number of working channels decreases, the OLT saves the result of this static bandwidth allocation; otherwise, the OLT abandons this static bandwidth allocation.

[0075] Simulation Results

[0076] Simulation scenario: There is 1 OLT, 256 ONUs, and 8 available working channels in the passive optical network. The static bandwidth of each ONU is equal. ONUs continuously register online and offline within 24 hours. The gradual change in the number of ONUs in each hour is uniform. For example: 6 o'clock (10 ONUs), 6:15 (15 ONUs), 6:30 (20 ONUs)...7 o'clock (30 ONUs). Table 1 shows the number of online ONUs at each time point. The performance of the following three static bandwidth allocation schemes was simulated. Simulation results Figure 2 In the figure, the horizontal axis is the time period, and the vertical axis is the average number of channels used by the online ONU within one hour.

[0077] Solution 1: When an ONU goes online or offline, the static bandwidth allocation results of all online ONUs remain unchanged.

[0078] Solution 2: When an ONU goes online or offline, all online ONUs will be re-allocated static bandwidth.

[0079] Solution 3: Low-complexity energy-saving static bandwidth allocation solution.

[0080] Table 1. Number of online ONUs at each time point

[0081]

[0082] The simulation results are as follows Figure 2 As shown in , the more channels are used, the greater the energy consumption. Figure 2 As can be seen, the energy-saving performance of our proposed solution 3 is higher than that of solution 1 and slightly lower than that of solution 2. At the same time, the adjustment complexity of our proposed solution 3 is lower than that of solution 2 and slightly higher than that of solution 1.

[0083] Although the above describes the illustrative specific embodiments of the present invention to facilitate understanding of the present invention by those skilled in the art, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concepts of the present invention are protected.

Claims

1. An energy-saving static bandwidth allocation method for a link rate configurable passive optical network, characterized in that: The following steps are involved: (1) Record the current status of the passive optical network; In a passive optical network, the optical line terminal (OLT) records the modulation format, working channel, and allocated bandwidth of the currently online optical network unit (ONU). At the same time, the OLT records the remaining time slots t of each working channel in the passive optical network. j , channel response and the set of ONUs allocated on each working channel, j = 1, 2, ..., M, where M is the number of working channels; when there is no ONU on a working channel, the remaining time slots of the channel are initialized to the bandwidth allocation period T DBA ; (2) Select static bandwidth allocation schemes with different strategies based on ONU requests; In a passive optical network, each ONU is monitored in real time. When an ONU needs to register online or log off offline, it will send a request message to the optical line terminal OLT. After receiving the request message sent by an ONU, the OLT first determines whether the content of the request message is a request to go online or a request to go offline. If it is a request to go online, it goes to step (3); If it is a request to go offline, jump to step (4); (3) Adjustment of static bandwidth allocation when ONU goes online and registers; (3.1) Assume that the ONU sending the request message is numbered k; the OLT reads the request message content and extracts the requested bandwidth B of the kth ONU. k and insertion loss λ k ; (3.2) OLT performs static bandwidth allocation for ONU No. k; (3.2.1) Sort the M working channels from 1 to M according to the channel response from high to low. For working channels with the same channel response, the working channel with the lower frequency is used first. Set the jth working channel as the initial allocation channel for the kth ONU, and initialize j = 1. (3.2.2) According to the insertion loss λ of the kth ONU k and the channel response of the jth working channel, determine the modulation format of the kth ONU on the jth working channel, and then calculate the link rate V of the kth ONU on the jth working channel k,j ; (3.2.3) Determine the remaining time slot t on the jth working channel j Is the bandwidth B sufficient to send the kth ONU? k , that is: t j ×V k,j ≥B k ×T DBA Is it satisfied? If so, go to step (3.2.4); otherwise, go to step (3.2.5); (3.2.4) Set the jth working channel as the working channel of the kth ONU, and set the kth ONU to the working channel according to the modulation format and working link rate V k,j Complete static bandwidth allocation, and the allocated static bandwidth is B k , the allocated time slot is T k =T DBA ×B k / V k,j At the same time, add the kth ONU to the ONU set on the jth working channel and update the remaining time slots of the jth working channel (3.2.5) Replace the j+1th working channel and perform bandwidth allocation for ONU No. k again according to steps (3.2.2) to (3.2.4); after all working channels are replaced, if all working channels cannot complete bandwidth allocation for ONU No. k, it means that ONU No. k has failed to go online and register, and the OLT abandons this static bandwidth allocation adjustment; (4) Adjustment of static bandwidth allocation when ONU goes offline; (4.1) Assume that the ONU sending the request message is numbered k; the OLT reads the request message content and extracts the modulation format, working channel and allocated bandwidth B of the kth ONU. k ; (4.2) OLT logs off the kth ONU; Assuming that ONU No. k is offline on working channel No. q, the transmission link rate V of ONU No. k is calculated based on the modulation format of ONU No. k on working channel No. q. k,q , OLT allocates bandwidth B k Update the remaining time slots of the qth working channel t q The remaining time slots of the qth working channel before the update; at the same time, the kth ONU that has been offline is deleted from the ONU set of the qth working channel; after that, the modulation format and working channel are no longer selected for the kth ONU that has been offline, and the allocated bandwidth B is k becomes 0; (4.3) The OLT performs static bandwidth allocation on the ONUs that are still online. (4.3.1) Sort the M working channels from 1 to M according to the channel response from highest to lowest. For working channels with the same channel response, the one with the lowest frequency will be used first. Then find the working channel with the lowest channel response that currently has an ONU working online. (4.3.2) Find the ONU set in the working channel with the lowest channel response, sort the ONUs in the ONU set from high to low according to their insertion loss and number them from 1 to N, then go to step (4.4) and re-allocate static bandwidth to the numbered ONUs in turn; (4.4) The OLT re-allocates static bandwidth for the nth ONU, where n = 1, 2, ..., N, and initializes n = 1; (4.4.1) Set the jth working channel as the initial allocation channel of the nth ONU, and initialize j = 1; (4.4.2) Based on the insertion loss of ONU No. n and the channel response of working channel No. j, determine the modulation format of ONU No. n on working channel No. j, and then calculate the link rate V of ONU No. n on working channel No. j. n,j ; (4.4.3) Determine the remaining time slot t on the jth working channel j Is the bandwidth B sufficient to send the nth ONU? n , that is: t j ×V n,j ≥B n ×T DBA Is it satisfied? If so, go to step (4.4.4); otherwise, go to step (4.4.5); (4.4.4) Set the jth working channel as the working channel of the nth ONU, and set the modulation format and link rate V of the nth ONU on the jth working channel. n,j Complete static bandwidth allocation, and the allocated static bandwidth is B n , the allocated time slot is T j =T DBA ×B n / V n,j ; Add the nth ONU to the ONU set on the jth working channel and update the remaining time slots of the jth working channel At the same time, the nth ONU is deleted from the ONU set in the working channel with the lowest channel response, and the remaining time slots of the working channel with the lowest channel response are updated. t 低 is the remaining time slot of the working channel with the lowest channel response before updating, V n,低 Indicates the link rate of ONU No. n on the working channel with the lowest channel response; Replace the n+1th ONU and perform bandwidth allocation for the n+1th ONU again according to steps (4.4.1) to (4.4.4) until bandwidth allocation for N ONUs is completed; (4.4.5) Change the j+1th working channel and complete the bandwidth allocation of the nth ONU on the j+1th working channel according to steps (4.4.1) to (4.4.4), and so on; (4.5) After N ONUs complete the static bandwidth allocation of all working channels, observe whether the total number of working channels used by all online ONUs in the passive optical network decreases. If the total number of working channels decreases, the OLT saves the result of this static bandwidth allocation; otherwise, the OLT abandons this static bandwidth allocation.

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